1. Field of the Invention
The present invention is generally related to marine propulsion systems that incorporate a jet pump and, more particularly, to a water jet propulsion system that, under certain conditions, incorporates one or more bypass channels that allow water to flow through a secondary channel to avoid passing through the impeller region of a primary flow channel.
2. Description of the Prior Art
Many different types of water jet propulsion systems are known to those skilled in the art. Some are mounted with an inlet opening formed in the hull of a boat. Others are mounted on the driveshaft housing of an outboard motor. All of the known water jet propulsion systems incorporate an inlet passage through which water is received, an impeller region where the water is accelerated by the blades of a rotating impeller, and a discharge region that can incorporate a nozzle. In some applications, the nozzle is moveable about a vertical axis to facilitate steering of a marine vessel incorporating the water jet propulsion system.
U.S. Pat. No. 5,123,867, which issued to Broinowski on Jun. 23, 1992, discloses a jet propulsion unit for a marine craft. A stream of water is induced in a converging inlet section and delivered as a steady laminar shaped flow regime to an impeller section where an impeller/diffuser vane combination and a converging annular volume enables operation of the vessel over a wide range of speeds and sea conditions without cavitation. Acceleration of water energized by the impeller through an interchangeable nozzle provides additional thrust and maneuverability. The propulsion unit additionally incorporates an arm-hole duct in the inlet housing for easy clean-up of any fouling and a bypass valve positioned upstream from the impeller to eliminate balling and drag caused thereby.
U.S. Pat. No. 4,004,541 which issued to Onal on Jan. 25, 1977, describes a pump which is used to propel the boat by means of a jet of water created by the pump. The pump includes a housing which is mounted exterior to the hull. A drive shaft and an impeller are mounted to rotate within the housing. The drive shaft extends through the transom of the boat and may be coupled directly to a gas turbine engine or other power generating device. The impeller is of the double suction type and includes ports for equalizing pressures on either side of the impeller at the suction positions thereof. The housing provides a double volute to receive the effluent from the impeller and direct it aft to a nozzle. Nozzle mechanisms are disclosed which provide easy steering and boat trim control under high thrust loads. A thrust reversal system is employed which directs the jet of water forward for stopping and reversing. A new scoop design is also included which reduces the possibility of air entrapment and loss of suction and increases the ram jet pressure for higher pump efficiency.
U.S. Pat. No. 4,073,257, which issued to Rodler, Jr. on Feb. 14, 1978, discloses a marine propulsion system for boats in which the thrust force center line is below the boat reaction center line to urge the propulsion system thrust line to tilt downwardly. The tilting of the propulsion system line downwardly lifts the stem of the hull to create a suitable vertical vector. As a consequence thereof, the boat is urged into a planing position for the reduction of drag on the boat in the lower speed range. At the higher speeds, dynamic water pressure reacts on the intake to urge the tilting of the thrust force center line upwardly toward a horizontal position to reduce the depth of the bow of the boat submerged in water for reducing the drag on the boat. A tension spring controls the angle of the tilting of the thrust force center line to attain the changeover at a selected speed for optimum operation.
U.S. Pat. No. 4,231,315, which issued to Tachibana et al on Nov. 4, 1980, describes a water jet propulsion unit for a personal watercraft. The propulsion unit is used for vessels which includes a water duct having an inlet and outlet portion and an impeller disposed in the water duct. The outlet portion has a variable outlet nozzle which can discharge water downwardly when desired to produce a lift force for lifting the stem of the vessel. The arrangement provides an improved rolling stability under a stationary condition and is also effective to decrease a drag force under the hump condition.
U.S. Pat. No. 5,700,170, which issued to Mataya on Dec. 23, 1997, discloses a variable diameter jet propulsion unit. An apparatus alters the diameter of the nozzle of a jet boat and thereby allows a user to maximize acceleration, top speed, fuel economy, or other factors. The apparatus allows a user to adjust the nozzle diameter opening, while the boat is moving, by an elastic annular hydraulic bladder that reduces the cross sectional area of a cone formed by a plurality of cone plates. The apparatus is compatible with steering and trim adjustment devices, and is located rearward of them. The apparatus is also compatible with existing jet boats, and provides a bowl adapter that may be attached to the impeller bowl of an existing jet. A steering collar attaches to the bowl adapter by two vertical pins in order to allow rotation to the left and right. Two horizontal pins on the steering collar support a nozzle front lock plate in a manner that allows vertical trim adjustment. The nozzle cone plates are mounted in a hinged manner to the nozzle front lock plate and the nozzle housing support. A spline assembly forces the nozzle cone plates to act in a symmetrical manner, and bridges the gap between adjacent nozzle cone plates when the nozzle is opened. This prevents the bladder from entering the gaps. An elastic block biases the nozzle cone plates radially outwardly, and opens the nozzle when the hydraulic bladder is not engaged.
U.S. Pat. No. 3,797,447, which issued to Stubblefield on Mar. 19, 1974, describes an inboard propulsion system for a boat. The system utilizes a water jet propulsion characterized by a pair of spaced nozzles which are each provided with individually controlled deflecting hoods to enable providing both a reverse thrust for backing the boat and to selectively reverse the water jet in a single nozzle to provide a turning force for steering the boat. Preferably, each of the nozzles is provided with a servo system which varies the effective opening of the nozzle in response to changes in the pressure differential between the intake pressure to the main impeller unit and the discharge pressure to the impeller unit to attempt to maintain a constant quantity flow from the nozzles independent or regardless of any variations in the intake pressure of the impeller unit.
U.S. Pat. No. 4,925,408, which issued to Webb et al on May 15, 1990, describes an intake and pump assembly for an aquatic vehicle. The intake and pump assembly includes an intake housing, a pump body, and a discharge nozzle. The intake housing is provided with an intake grill and flow director. The impeller is surrounded by a wear ring. A vane in integrally formed within the pump body. The drive shaft assembly is provided with couplers and ball guides of resilient material which interconnect the component parts of the drive shaft assembly and absorb shock and misalignment. Stacked washers are provided for adjustment purposes.
U.S. Pat. No. 3,943,876, which issued to Kiekhaefer on Mar. 16, 1976, discloses a water jet boat drive. The water jet is mounted rigidly entirely outboard of the boat and driven from an inboard engine by an interconnecting shaft through the transom. The tail nozzle is mounted concentric of and spaced from the pump chamber of the jet and extends rearwardly therefrom and axially thereof. A butterfly trim vane is pivotally mounted on a transverse horizontal axis in the tail nozzle and is adapted to close the nozzle for blocking the jet and compelling a reverse flow of the water from the pump through passages between the pump chamber and tail nozzle. A steering vane is mounted on a vertical axis rearwardly of the tail nozzle and carries a rudder disposed beneath the jet steering vane for steering during reversal of the jet. The engine exhaust is introduced to the jet stream within the tail nozzle and has a bypass operable during reversing of the jet stream.
U.S. Pat. No. 5,476,401, which issued to Peterson et al on Dec. 19, 1995, describes a compact water jet propulsion system for a marine vehicle. It incorporates an unconventional and compact design which includes a short, steep, hydrodynamically designed inlet duct that is adapted for mounting to the surface of the vehicle hull and extending internally thereof, a water jet pump having an inlet end attached to the outlet end of the inlet duct, a motor for rotating the pump impeller, a drive shaft located completely outside of the flow path connecting the motor with the pump impeller, a flow passage for discharging accelerated flow received from the pump in a generally rearward direction, and a steering and reversing mechanism pivotably mounted about a substantially vertical axis to the aft portion of the vehicle hull for redirect accelerated flow received from the outlet nozzle so as to provide maneuvering capability to the vehicle.
U.S. Pat. No. 5,421,753, which issued to Roos, on Jun. 6, 1995, describes a marine jet drive which has improved operations, especially with regard to having efficient adaptation to propulsion engine and hull design. It has a drive shaft with a flexible coupling at each end, internal to the jet drive. It also has a through-the-nozzle engine exhaust and a simplified combined means of steering and reversing. In incorporates a controllable nozzle aperture and trim control with a combination reverse flow deflector and trim plate. It also comprises a means to disengage the engine from the jet to obtain a true neutral condition. The jet drive has protection from and removal of debris in the water intake duct and generally provides for fewer overhauls, easier serviceability and lighter weight.
U.S. Pat. No. 4,004,541, which issued to Onal on Jan. 25, 1977, discloses a jet boat pump. The centrifugal pump is used for a boat and is used to propel the boat by means of a jet of water created by the pump. The pump includes a housing which is mounted exterior to the hull. A drive shaft and an impeller are mounted to rotate within the housing. The drive shaft extends through the transom of the boat and may be coupled directly to a gas turbine engine or other power generating device. The impeller is of the double suction type and includes ports for equalizing pressure on either side of the impeller at the suction positions thereof. The housing provides a double volute to receive the effluent from the impeller and direct it aft to a nozzle. Nozzle mechanisms are disclosed which provide easy steering and boat trim control under high thrust loads. A thrust reversal system is employed which directs the jet of water forward for stopping and reversing. A scoop design is included which reduces the possibility of air entrapment and loss of suction and increases the ram jet pressure for higher pump efficiency.
U.S. Pat. No. 5,536,187, which issued to Nanami on Jul. 16, 1996, discloses an outboard jet drive for watercraft. It is intended for use with a jet propelled watercraft which has an outboard motor type of jet propulsion unit. The propulsion is disposed in substantial part forwardly of the transom and beneath the undersurface of the hull for improving its pumping efficiency. The jet propulsion unit is driven by a transmission including a drive shaft having a pivotal joint. The jet propulsion unit is pivotal relative to the engine about an axis containing the axis of the universal joint so that the water inlet opining may be swung inwardly through an opening in the undersurface of the hull which is above the water level for clearing foreign objects from the jet propulsion unit water inlet opening.
Most jet propulsion systems known to those skilled in the art exhibit two characteristics which can be disadvantageous under certain conditions. First, they tend to experience high inlet pressures at high boat speeds. The increase in inlet pressure has a deleterious effect on the efficiency of the jet pump at higher speeds. A second characteristic of known jet propulsion systems is that they can lose their ability to steer the marine vessel when the throttle is suddenly reduced. It would therefore be significantly beneficial if a jet propulsion system could be provided in which these two disadvantageous characteristics are significantly reduced or eliminated. In other words, a jet propulsion system which does not exhibit significantly decreased efficiency at high speed and which does not lose steering authority when the throttle is suddenly reduced to idle speed when the boat is moving would represent a significant improvement in the art of marine propulsion systems that incorporate jet drives.